In an apparatus for recording video signals into a recording medium and reading-out video signals from the recording medium, one or both of an aperture compensation and a noise cancellation are generally carried out.
A conventional aperture compensation circuit comprises a high-pass filter connected at its input to an input terminal group, a coring circuit connected at its inputs to a threshold value input terminal group and an output of the high-pass filter, and an adder for adding an output signal of the coring circuit and a signal of the input terminal group to produce an added signal which is supplied to an output terminal group.
In operation, a high frequency component of a digital video luminance signal which is supplied from the input terminal group is passed through the high-pass filter, and a low level component of the high frequency component video luminance signal is cut-off in the coring circuit in the comparison with a threshold signal applied to the threshold value input terminal group. The high frequency component video luminance signal including no low level component is added in the adder with the digital video luminance signal directly supplied from the input terminal group to produce the added signal which is supplied to the output terminal group.
A conventional noise cancellation circuit comprises a high-pass filter connected at its input to an input terminal group, a limiter circuit connected at its inputs to an output of the high-pass filter and a threshold value input terminal group, and a subtracter connected at its inputs to an output of the limiter circuit and the input terminal group and at its output to an output terminal group.
In operation, a digital video luminance signal is applied to the input terminal group, and a high frequency component thereof is passed through the high-pass filter. A component of the high frequency component video luminance signal higher in its level than a threshold signal applied to the threshold value input terminal group is cut-off in the limiter circuit. An output signal of the limiter circuit is supplied to the subtracter, in which the digital video luminance signal is subtracted by the output signal of the limiter circuit. The subtracted signal is supplied to the output terminal group.
Consequently, a high frequency component of the digital video luminance signal is emphasized in the aperture compensation circuit, and a noise component is attenuated in the noise cancellation circuit.
According to the conventional aperture compensation circuit, however, there is a disadvantage that a noise component of the digital video luminance signal supplied directly from the input terminal group is not removed and remains included therein, where the aperture compensation circuit is solely used, because the directly supplied digital video luminance signal is added in the adder to the output signal of the coring circuit, in which a component lower than the threshold signal level is removed as a noise component.
According to the conventional noise cancellation circuit, further, there is a disadvantage that an edge of the output signal is smaller at the output terminal group than an edge of the digital video luminance signal supplied directly from the input terminal group, where the noise cancellation circuit is solely used, because the directly supplied digital video luminance signal is subtracted in the subtracter by the output signal of the limiter circuit, in which a component higher than the threshold signal level is removed as an edge component from the output signal of the high-pass filter. Therefore, the edge component is not sufficiently emphasized.
Even if the aperture compensation circuit and the noise cancellation circuit are both used, the emphasizing effect of an edge component is not sufficiently large for the same reason as set forth in the sole use of the noise cancellation circuit. Where the both circuits are used, there is resulted in a further disadvantage that a circuit scale becomes large, because the adder and the subtracter are required to be used. For instance, where the circuits are structured by a semiconductor integrated circuit (defined "IC" hereinafter), a chip area is increased, so that a fabricating cost becomes high.